Polybutylene modified masterbatches for impact resistant polypropylene

ABSTRACT

An impact resistant polypropylene prepared with a masterbatch comprising an uncured elastomer, a butene-1 polymer and an optional comodifier such as high density polyethylene possesses improved weld line strength and other properties.

BACKGROUND OF THE INVENTION

This invention relates to polybutylene modified masterbatches used inthe preparation of impact resistant polypropylene with enhancedproperties. More particularly, a masterbatch comprising an elastomer, abutene-1 polymer and an optional co-modifier affords a polypropylenewith improved properties, notably impact resistance, elongationproperties and weld line strength.

High impact polypropylene (HIPP) is conventionally produced by blendinginto polypropylene an impact blend consisting of a rubber such as anethylene-propylene-diolefin elastomer (EPDM) and a co-modifier such ashigh density polyethylene (HDPE). The impact blend is typically "letdown" into polypropylene by mixing pellets of the blend andpolypropylene and extruding the mixture. While the addition of a rubbergenerally results in improved impact strength, the resulting HIPP mayexhibit loss of weld line strength or ductility. Weld lines occur ininjection molded articles in which flow fronts of injected polymer meetin the mold, either because polymer is injected through multiple gatesor because injected polymer flow is parted, as by an insert in the mold.The line formed where the separate portions of polymer meet in the moldis the weld line. Ideally this is not perceptible and has the samestrength as the remainder of the article. In the case of polymercompositions whose impact is improved by added elastomers, the weld linemay be significantly weaker. It has now been discovered thatsubstitution of a butene-1 polymer for all or portion of the comodifierused with the rubber in the impact blend, affords HIPP while avoidingthese undesirable property changes in the finished product.

U.S. Pat. No. 4,078,020 discloses a thermoplastic composition comprisingpolypropylene, polybutylene and from 20 to 80% by weight of anelastomeric material such as an EPDM. The three components are blendedto flux in a mixer; a masterbatch technique is not used. The compositionhas a higher rubber content and very low stiffness values, and does notexhibit the enhanced weld strength of HIPP prepared according to thepresent invention.

U.S. Pat. No. 3,455,871 discloses a masterbatch technique where butene-1polymers are used as carriers to disperse additives in other polymers.The additives are described as non-olefinic materials such as pigmentsand lubricants, as opposed to the rubber or rubber/co-modifier mixedwith the butene-1 polymer in the masterbatches herein.

SUMMARY OF THE INVENTION

This invention is directed to a masterbatch composition for theproduction of impact resistant polypropylene which comprises:

(a) about 25 to 70% by weight of an uncured elastomer selected from thegroup consisting of ethylene-propylene copolymer,ethylene-propylene-diene terpolymer and mixtures thereof; and

(b) about 30 to 75% by weight of an isotactic butene-1 polymer selectedfrom the group consisting of butene-1 homopolymer, butene-1-ethylenecopolymer and mixtures thereof.

Alternatively, this invention is directed to a masterbatch compositionwherein the uncured elastomer is present in an amount of from about 20to 70% by weight, the butene-1 polymer is present in an amount of fromabout 10 to 40% by weight, and which additionally comprises:

(c) about 10 to 40% by weight of a co-modifier selected from the groupconsisting of high density polyethylene, propylene-ethylene copolymer,polypropylene and mixtures thereof.

This invention is also directed to a method of making an impactresistant polypropylene which comprises blending about 75 to 95% byweight of polypropylene with about 5 to 25% by weight of a masterbatchcomprising either of the above-noted compositions. Further, theinvention is directed to an impact resistant polypropylene prepared bythe described masterbatch processes.

The masterbatch compositions and processes herein afford a polypropylenewhich may be prepared using very light compounding and exhibits improvedproperties over a wide range of proportions of the various components.These property enhancements do not normally result when the butene-1polymer is co-compounded with a conventional rubber/co-modifier impactblend or when the butene-1 polymer is co-compounded with a rubber and/orco-modifier without use of a masterbatching technique. Incorporation ofthe butene-1 polymer is the masterbatch maximizes dispersion whencompounded in the polypropylene matrix and offers convenience andeconomy in that the need for intensive mixing with the polypropylene isavoided and that only one material, the masterbatch itself, must beformulated in the polypropylene.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Component (a) of the masterbatch composition is an elastomer selectedfrom the group consisting of ethylene-propylene copolymer,ethylene-propylene-diene terpolymer and mixtures thereof. The elastomeris not cured or cross-linked; no free radical generating agent is usedin its preparation or during blending. The ethylene-propylene copolymer,typified by saturated EPM, and the ethylene-propylene-diene terpolymer,typified by unsaturated EPDM, are commercially available and methods fortheir preparation are well known in the art as shown in, for example,U.S. Pat. No. 4,033,889. Suitable copolymers contain from about 30 to 80weight percent, preferably 40 to 70 weight percent, of ethylene.Suitable terpolymers contain from about 30 to 80 weight percent,preferably about 40 to 70 weight percent, of ethylene, from about 18 to70 weight percent, preferably about 30 to 60 weight percent, ofpropylene, and from about 0.2 to 10 weight percent, preferably about 1to 3 weight percent of a non-conjugated diene or mixture thereof. Thepreferred dienes are 1,4-hexadiene, 5-ethylidene- 2-norbornene anddicyclopentadiene, with 1,4-hexadiene more preferred. Thecharacteristics of the elastomer (rubber) used may affect the selectionof a preferred masterbatch composition; suitable proportions of eachcomponent may be readily determined by routine experimentation. Ingeneral however, a partially crystalline rubber (e.g., 60 to 70% byweight ethylene content) is more suitable for use in masterbatches withhigher rubber content; more amorphous rubbers (e.g., 40 to 55% by weightethylene content) may cause such handling problems as excessivetackiness and/or a tendency towards "blocking".

Component (b) of the masterbatch composition is an isotactic butene-1polymer selected from the group consisting of butene-1 homopolymer(polybutylene), butene-1-ethylene copolymer and mixtures thereof.

The polymers used are suitably crystalline thermoplastic butene-1polymers with molecular weights above 20,000. Suitable isotacticbutene-1 polymers are commercially available and methods for theirpreparation are well known in the art as shown, for example, in U.S.Pat. No. 3,362,940. Suitable copolymers contain up to about 15 percentby weight, preferably up to 10 percent by weight of ethylene. Ingeneral, a butene-1-ethylene copolymer is suitably used as the butene-1polymer component when increased weld strength of the finished impactresistant polypropylene is a primary consideration.

In the masterbatches of the invention which include a comodifier(component [c]), the co-modifier is selected from the group consistingof high density polyethylene (HDPE), propylene-ethylene copolymer,polypropylene (PP) and mixtures thereof. In general, the use of HDPE asthe comodifier will result in finished polypropylenes showing higherimpact strength values. The co-modifiers are commercially available andmethods for their preparation are well known in the art. Thepropylene-ethylene copolymers are suitably non-elastomeric random orso-called "block" copolymers. The random propylene-ethylene copolymerssuitably contain up to about 6, preferably up to 4 percent by weight ofethylene. The "block" propylene-ethylene copolymers are produced, forexample, by sequential polymerization of propylene alone and, typically,a propylene-ethylene mixture, and may be an intimate in-situ blend withrelatively few truly "blocked" molecules. The "block" copolymerssuitably contain up to about 14, preferably up to 8 percent by weight ofethylene. The polypropylene is suitably crystalline isotacticpolypropylene. The polypropylene or propylene-ethylene copolymer withwhich the masterbatch is blended may be conveniently used as aco-modifier in the instance.

Masterbatches which do not include a co-modifier component compriseabout 25 to 70% by weight, preferably 50 to 67% by weight, of theuncured elastomer, and about 30 to 75% by weight, preferably 33 to 50%by weight, of the butene-1 polymer. Masterbatches which include aco-modifier component comprise about 20 to 70% by weight, preferably 33to 67% by weight, of the uncured elastomer, about 10 to 40% by weight,preferably 15 to 33% by weight, of the butene-1 polymer, and about 10 to40% by weight, preferably 15 to 33% by weight of the co-modifier. Inmasterbatches including a co-modifier component, the amounts of butene-1polymer and co-modifier used need not be equivalent. The masterbatchcompositions are typically formulated by blending the components in aBanbury mixer or other intensive mixer.

This invention is also directed to a method of making an impactresistant polypropylene which comprises blending about 75 to 95% byweight, preferably 77 to 90% by weight, of polypropylene, with about 5to 25% by weight, preferably 10 to 23% by weight, of a masterbatchcomposition, with or without a co-modifier, as defined herein. Thisinvention is further directed to impact resistant polypropylenesprepared by the methods defined herein. Crystalline isotacticpolypropylene is the preferred polypropylene although thenon-elastomeric random or so-called "block" propylene-ethylenecopolymers (described previously as suitable co-modifiers) may also beused. The polypropylenes are commercially available and methods fortheir preparation are well known to those skilled in the art. The impactresistant polypropylene of the invention is typically formulated bymixing, e.g. tumbling, pellets of the polypropylene and the masterbatchand extruding the mixture. The masterbatching technique according to theinvention affords a good, uniform dispersion of the rubber (elastomer)component throughout the polypropylene matrix. Further, the use of verylight compounding in a less intensive mixer, e.g., a single screwextruder or screw-type molding machine, is made possible; this, in turn,allows for the convenience and economy of higher throughput levels. Ifdesired, various conventional fillers, stabilizers, processing agentsand/or pigments may be included in the polymer.

Impact resistant polypropylene prepared according to the inventionexhibits a wide variety of improved properties over polypropylenesprepared with masterbatches not containing a butene-1 polymer orpolypropylenes prepared by co-compounding all components without use ofthe masterbatch technique. The polypropylene of the invention maydemonstrate, for example, improvement in impact resistance, impact shearsensitivity, weld line strength, elongation properties (ductility),spiral flow and/or toughness. The finished polypropylene may be used invarious fabrication equipment, including molding, extrusion, forming andblow molding equipment, for the manufacture of molded articles, pipe,film and other items.

The invention is illustrated further in the following examples, whichare not to be construed as limiting its scope. In the examples, thecomponents are denoted as follows:

PB-A--butene-1-ethylene copolymer (8%w ethylene) with melt index of 0.2

PB-B--butene-1 homopolymer with melt index of 1.8

PB-C--butene-1-ethylene copolymer (8%w ethylene) with melt index of 1.8

PP-A--isotactic 5 melt flow propylene homopolymer

PP-B--isotactic 12 melt flow propylene homopolymer.

The melt index and melt flow, as used herein, were measured by ASTMD1238 Conditions E and L, respectively. The rubber used was an EPDMterpolymer consisting essentially of 50 weight % ethylene, 48 weight %propylene and 2 weight % 1,4-hexadiene. The HDPE used had a melt indexof 2 and a specific gravity of 0.96.

EXAMPLE I

In this series of experiments, impact resistant polypropylene wasprepared by compounding polypropylene with 23%w of a masterbatchcontaining a butene-1-ethylene copolymer in a Prodex single screwextruder. The masterbatches had been separately prepared by Banburycompounding of an EPDM terpolymer rubber, the butene-1-ethylenecopolymer and a co-modifier consisting of HDPE or an additional portionof the same polypropylene. An experiment using a conventional 50:50 EPDMrubber/HDPE masterbatch was run as a control (Composition A). Thefinished product resistant polypropylenes were evaluated and the resultsare shown below in Table I. The falling weight impact strength (FWIS)test was conducted using a 1.27 cm tup radius, 66 cm drop and variableweight (ASTM D3029 modified). The weld strength (ASTM D638 modified) wasdetermined using double-gated specimens at 12.7 cm/minute. The spiralflow was determined with an Archimedes flat spiral with a 1.27 by 0.25cm cross-sectional area. The results from the evaluation of the finishedimpact resistant polypropylenes are shown below in Table I.

                  TABLE I                                                         ______________________________________                                        Evaluation of Impact Resistant Polypropylene Prepared                         with Masterbatches Containing Butene-1 Polymers                               Masterbatch Composition %                                                                              A      B      C                                      ______________________________________                                        EPDM Rubber             11.5   11.5   11.5                                    HDPE                    11.5   6.5     --                                     PP-A                     --     --    6.5                                     PB-A                     --    5      5                                       Basestock : PP-A        77     77     77                                      Properties                                                                    FWIS (-20° C.),                                                        Minimum Shear, Joules   20     21     18                                      Maximum Shear, Joules   15     21     16                                      Weld Strength, %        3      5      6                                       Spiral Flow (230° C., 6895 kPa), cm.                                                           47.5   48.7   51.3                                    Tensile Yield at 5 mm/min, MPa                                                                        21     19     19                                      (ASTM D638)                                                                   Yield elongation at 5 mm/min, %                                                                       10     11     9                                       (ASTM D638)                                                                   Flexural Modulus (50 mm span) at                                                                      950    800    825                                     1.3 mm/min, MPa (ASTM D790)                                                   Izod Impact Strength (ASTM D256)                                              at 23° C., J/m   220    560    60                                      at -18° C., J/m  19     15     15                                      Heat Deflection Temperature (455 kPa), °C.                                                     90     78     89                                      (ASTM D648)                                                                   ______________________________________                                    

A comparison of Compositions B and C, which contain a butene-1 polymer,with the control Composition A, shows that impact resistantpolypropylene prepared using a butene-1 polymer has substantiallyimproved weld strength, good practical impact (FWIS), minimal impactshear sensitivity and somewhat improved flow. The stiffness (flexuralmodulus), tensile yield and heat distortion were negatively affected byincorporation of the butene-1 polymer.

EXAMPLE II

In this series of experiments, impact resistant polypropylene wasprepared by compounding a polypropylene (PP-B) with 23%w of variousimpact masterbatches in a Sterling 1.25 inch extruder. The masterbatcheshad been separately prepared by Banbury compounding of an EPDMterpolymer rubber, a butene-1 polymer and optionally an HDPEco-modifier. An experiment using the conventional 50:50 EPDM rubber/HDPEmasterbatch of Example I was run as a control (Composition D). Themechanical properties of the finished impact resistant polypropylenesare shown below in Table II. Testing was conducted according to themethods described in Example I and Table I.

All four of the products prepared with masterbatches containing butene-1polymers showed improved weld strength over control Composition D,although declines in the 1% secant modulus were also observed. Thetwo-component masterbatch products, Compositions E and H, showed greaterweld strength enhancements than the three-component masterbatchproducts, Compositions F and G. The Battenfeld Izod test data, fordouble-gated specimens, a combined measure of weld and impact strength,showed better results at both temperatures for all the butene-1 polymercontaining products than for the control Composition D. On the otherhand, the New Britain standard Izod test data for single-gated specimensshowed comparable results for the control and the products containingbutene-1 polymers. Compositions E through H generally gave improvedultimate elongation values and greatly improved Gardner impact values;these properties are direct measures of toughness. When the propertiesof each blend were numerically ranked relative to the others,Composition G was found to have the best overall performance, althoughthis does not necessarily mean it would be the composition of choice forall specific applications.

EXAMPLE III (Not According to the Invention).

In this series of experiments, pellets of a butene-1-ethylene copolymer,an optional HPDE co-modifier and polypropylene and a ground EPDMterpolymer were mixed and co-compounded in a Prodex single screwextruder, without use of a masterbatch technique. Testing was conductedaccording to the methods described in Example I and Table I. Spiralflows and both FWIS impact plaques were prepared on a Van Dorn screwtypeinjection molding press. The double gated tensile bar for weld strengthwas prepared on a Battenfeld molding press. In preparing the blends, theground EPDM terpolymer was dusted with 3%w of a 10 melt flowpolypropylene powder to prevent blocking. The compositions andproperties of the resultant impact resistant polypropylene are shownbelow in Table III. A comparison of Composition J with Composition B inTable I demonstrates that impact resistant polypropylene prepared with amasterbatch technique exhibits improved weld strength and flow.

                                      TABLE II                                    __________________________________________________________________________    Evaluation of Impact Resistant Polypropylene                                  with Masterbatches Containing Butene-1 Polymers                               __________________________________________________________________________                          Battenfeld Injection Molder.sup.(a)                                           Weld                                                    Impact Masterbatch Composition, % w                                                                 Strength                                                                           Unotched Izod,                                                                         J/m                                       Comp.                                                                             EPDM Rubber                                                                           HDPE                                                                              PB-B                                                                             PB-C                                                                             %.sup.(c)                                                                          -18° C.                                                                         23° C.                             __________________________________________________________________________    D   50      50  -- -- 2.0  101       96                                       E   50      --  -- 50 4.5  112      123                                       F   50      25  -- 25 3.3  123      133                                       G   50      25  25 -- 3.0  123      128                                       H   50      --  50 -- 4.0  123      155                                              New Britain Injection Molder.sup.(b)                                          1% Secant                                                                           Yield                                                                             Yield                                                                             Ultimate                                                                           Gardner                                                                             Unnotched                                            Modulus,                                                                            Tensile                                                                           Elong.                                                                            Elong.                                                                             Impact.sup.(d)                                                                      Izod, -18°  C.;                        Comp.  MPa   MPa %   %    -30° C.; J                                                                   kJ/m                                          __________________________________________________________________________    D      1160  26.4                                                                              9    16  6.4   1.2                                           E       896  24.1                                                                              12  185  6.3   1.0                                           F       965  24.8                                                                              13  170.sup.(e)                                                                        7.3   1.3                                           G      1080  26.5                                                                              10  173.sup.(f)                                                                        8.0   1.2                                           H      1020  26.1                                                                              10  134  13.0  0.80                                          __________________________________________________________________________     .sup.(a) Molding temperature set at about 210° C. or above;            doublegated tensile specimen                                                  .sup.(b) Molding temperature set at about 204° C. or above             .sup.(c) Rate of strain 127 mm/min                                            .sup.(d) Disk: 51 mm × 32 mm (test with ring in)                        .sup.(e) 95% confidence limits ± 103%                                      .sup.(f) 95% confidence limits ± 78%                                  

                  TABLE III                                                       ______________________________________                                        Evaluation of Co-compounded Impact Resistant                                  Polypropylene Prepared without Masterbatching                                              Co-Compounded                                                                 J       K         L                                              ______________________________________                                        Composition, %                                                                EPDM Rubber    11.5      11.5      11.5                                       HDPE           6.5       --        11.5                                       PB-A           5         11.5      5                                          PP-A           77        77        72                                         Compounding                                                                   Equipment      Prodex    Prodex    Prodex                                     Properties                                                                    FWIS at -20° C., Joules                                                Minimum shear  26        28        32                                         Maximum shear  26        31        34                                         Weld strength, %                                                                             3.5       4         3                                          Spiral flow, cm.                                                              (230° C. 6895 kPa)                                                                    46.2      46.9      45.1                                       ______________________________________                                    

We claim as our invention:
 1. A masterbatch composition for theproduction of impact resistant polypropylene which consists essentiallyof:(a) about 20 to 70% by weight of an uncured elastomer selected fromthe group consisting of ethylene-propylene copolymer,ethylene-propylene-diene terpolymer and mixtures thereof; (b) about 10to 40% by weight of an isotactic butene-1 polymer selected from thegroup consisting of butene-1 homopolymer, butene-1-ethylene copolymerand mixtures thereof; and (c) about 10 to 40% by weight of high densitypolyethylene.
 2. The masterbatch composition defined in claim 1, whichconsists essentially of:(a) about 33 to 67% by weight of the uncuredelastomer; (b) about 15 to 33% by weight of the butene-1 polymer; and(c) about 15 to 33% by weight of high density polyethylene.
 3. Themasterbatch composition defined in claim 2, wherein the uncuredelastomer is an ethylene-propylene-diene terpolymer.
 4. The masterbatchcomposition defined in claim 2, wherein the butene-1 polymer is abutene-1-ethylene copolymer.
 5. A method of making an impact resistantpolypropylene which comprises blending about 75 to 95% by weight ofpolypropylene with about 5 to 25% by weight of a masterbatch consistingessentially of:(a) about 20 to 70% by weight of an uncured elastomerselected from the group consisting of ethylene-propylene copolymer,ethylene-propylene-diene terpolymer and mixtures thereof; (b) about 10to 40% by weight of an isotactic butene-1 polymer selected from thegroup consisting of butene-1 homopolymer, butene-1-ethylene copolymerand mixtures thereof; and (c) about 10 to 40% by weight of high densitypolyethylene.
 6. The method defined in claim 5, which comprises blendingabout 77 to 90% by weight of polypropylene with about 10 to 23% byweight of the masterbatch composition.
 7. An impact resistant, weld linecontaining, injection molded article prepared from a polypropylenecomposition prepared by the process described in claim
 5. 8. An impactresistant, weld line containing, injection molded article prepared froma polypropylene composition prepared by the process described in claim6.